In electrohydraulic systems which include a plurality of electrohydraulic devices, such as servo actuators, motors and pumps, it is conventional practice to couple all of such devices to a remote central or master controller for coordinating device operation to perform desired tasks. Motors and actuators may be employed, for example, at several coordinated stages of a machine tool line for automated transfer and machining of parts at a series of work stations. In another typical application, the moving components of an earth excavator may be coupled to electrohydraulic actuators controlled by a central controller responsive to operator lever or joystick inputs.
Conventionally, the central or master host controller may comprise a programmable logic controller or a personal computer. The host controller is coupled by digital-to-analog converters to the various remotely-positioned electrohydraulic devices through low speed serial or parallel input/output (I/O) ports for supplying control signals thereto. For closed-loop operation a sensor is positioned at each eletrohydraulic device for sensing operation thereof, and feeds a corresponding sensor signal to the remote central controller through an analog-to-digital converter, appropriate signal conditioner and the same low speed I/O port.
Thus, in a system which embodies a plurality of electrohydraulic devices, a substantial quantity of electrical conductors must be provided for feeding individual control signals to the various devices and returning sensor signals to the central controller. Such conductors interfere with system design and operation, and are subject to failure, adding to the expense and complexity of the overall system. Furthermore, low speed serial or parallel I/O between the central host controller and the various device controllers severely limits speed of operation.
It is therefore a general object of the present invention to provide an electrohydraulic servo system which exhibits reduced cost and complexity as compared with prior art systems of the character described. In furtherance of the foregoing, a more specific object of the invention is to provide a system of the described character wherein each of the system electrohydraulic devices is controlled by a dedicated local microprocessor-based controller adapted to communicate with a high speed central controller over a common data bus for thereby distributing control of the several electrohydraulic devices and reducing interconnection cost and complexity while maintaining overall system coordination and speed capabilities.